Apps Script using the Todoist API to set a due date of today on any tasks in the Alexa To-do List and Inbox projects that do not have a due date. For instructions on setting this up see https://ithoughthecamewithyou.com/post/using-the-todoist-api-to-set-a-due-date-on-the-alexa-integration-todo-list-with-apps-script

Code.gs

var ApiToken = '';

function checkForAlexaTasksWithNoDate() {
  processProject('Alexa To-do List');
  processProject('Inbox');
}

function processProject(projectName) {
  var id = getAlexaToDoListId(projectName);
  var tasks = getAlexaToDoListTasks(id);
  
  var len = tasks.length;
  for(var i = 0; i < len; i++) {
    if (!tasks[i].due) {
      setTaskDueToday(tasks[i].id)
    }
  }
}

function setTaskDueToday(taskId) {
  var request = {
    'due_string': 'Today'
  };

  UrlFetchApp.fetch('https://api.todoist.com/rest/v2/tasks/' + taskId, {
    headers: {
      Authorization: 'Bearer ' + ApiToken
    },
    'method' : 'post',
    'contentType' : 'application/json',
    'payload' : JSON.stringify(request, null, 2)
  });
}

function getAlexaToDoListTasks(id) {
 var response = UrlFetchApp.fetch('https://api.todoist.com/rest/v2/tasks?project_id=' + id, {
    headers: {
      Authorization: 'Bearer ' + ApiToken
    }
  });

  return JSON.parse(response.getContentText());
}

function getAlexaToDoListId(projectName) {
  var response = UrlFetchApp.fetch('https://api.todoist.com/rest/v2/projects', {
    headers: {
      Authorization: 'Bearer ' + ApiToken
    }
  });

  var json = JSON.parse(response.getContentText());

  var len = json.length;
  for(var i = 0; i < len; i++) {
    if (json[i].name == projectName) {
      return json[i].id;
    }
  }

  throw 'Could not find project';
}